code: def test_dissolve_retains_existing_crs(nybb_polydf):
      assert nybb_polydf.crs is not None
      test = nybb_polydf.dissolve("manhattan_bronx")
      assert test.crs is not None
  
imports: import warnings
  import numpy
  import pandas
  import geopandas
  from geopandas import GeoDataFrame, read_file
  from pandas.testing import assert_frame_equal
  import pytest
  from geopandas._compat import PANDAS_GE_15, PANDAS_GE_20
  from geopandas.testing import assert_geodataframe_equal, geom_almost_equals
label_desc: Use image node_id 6 for calling a global function with example usage: test_dissolve_retains_existing_crs(nybb_polydf) without return types